This is a great idea that I found on the Sims 2 Official BBS. This is a direct quote of his post, which can be found [here].
A great idea and thanks to Pinstar for inventing it!

The challenge: Make a family the strongest it can be over 10 generations. The Rules: Start with a single adult sim made with the create-a-sim or bodyshop, male or female. Pick any aspiration. Assign personality points as you want.

Start the family on an empty 5X5 Lot.

When you marry or move sims in, you may only marry or move in townies or NPCs.

Children may move out if you want but you must keep at least one child in the home to continue the legacy.

When children grow into teenager and you are asked to pick an aspiration, roll a six sided dice
1: Wealth
2: Knowledge
3: Family
4: Romance
5: Popularity
6: Pick one yourself

This is to give some challenges and variety as you play through the generations.

The 10th generation child must be able to trace family back up to the original sim by blood.

You may NOT turn ageing off
You may use the elixir of life, but use caution, as you may suffer the jump bug.
You may use any other normal asperation reward objects.
You may NOT use any kinds of cheats or mood trainers.
You may NOT use any "special" objects such as the platinum-maxing painting.
You may use any maxis-made objects, and any 3rd party skins/wallpapers/floors etc.
You may NOT use the new twins or abduction patches.

No reloading after bad events (bad chance cards or accidental deaths) Restarting after a bad bug or a glitch IS allowed. Just as useing the move_objects cheat is allowed for bugged objects.

Hacks ok for bugs.

At the end of the challenge (10 generations or after the family line is broken) score your family on the following terms.

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I'm not keeping score, so I won't have that here. :)
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Of course there is NO way for anyone to enforce the rules or scoring, so the whole contest is on the honor system. I'm just putting this contest out here as a fun challenge among simmers, not an "I'm better than you" ego-fest. I look foreward to seeing everyone's scores while I start cracking on my own Legacy family. Good Luck!